Trump Says He Will Not Talk to North Korea. Experts Fear He Will.

Previous presidents avoided that trap, Mr. Russel said, even if Bill Clinton briefly contemplated meeting Mr. Kim’s father, Kim Jong-il. But Mr. Trump brings a deal-maker’s swagger to the North Korea issue that his predecessors did not. He has in the past expressed a willingness to sit across a table from the willful young scion of North Korea’s ruling family.

“I would speak to him,” Mr. Trump said during the presidential campaign. “I would have no problem speaking to him.” Last April, he said, “If it would be appropriate for me to meet with him, I would absolutely; I would be honored to do it.”

While the Pentagon has drawn up options for a military strike on the North, officials concede it would be all but impossible, given the retaliation it would provoke and the calamitous casualties that would result. Stephen K. Bannon, Mr. Trump’s former chief strategist, reflected that internal consensus when he told The American Prospect, “There’s no military solution. Forget it.”

That leaves diplomacy, which Secretary of State Rex W. Tillerson and other officials have made clear is still the administration’s preferred course. If North Korea curbs its behavior, Mr. Tillerson said recently, there is a “pathway to sometime in the early future having some dialogue.”

Hours after Mr. Trump ruled out talks on Twitter, Defense Secretary Jim Mattis contradicted him. “We’re never out of diplomatic solutions,” he told reporters. In Geneva, Robert A. Wood, the American ambassador to the Conference on Disarmament, said the United States remained open to dialogue. “We do not seek to be a threat to the Kim Jong-un regime,” he said.

Trying to explain Mr. Trump’s tweet, Mr. Wood, who was once the State Department’s acting spokesman, said, “What the president is saying is that he doesn’t see talking as solving this problem and part of the reason is that the North is not interested in dialogue.”

Indeed, Mr. Trump’s sudden hostility to talks appeared to be less a reversal of his previous statements than an expression of frustration with Mr. Kim’s continued belligerence. Days after Mr. Trump praised him for his newfound restraint, Mr. Kim lobbed a missile over Japan.

For now, a Trump-Kim summit remains a far-fetched notion. Even if North Korea was interested in speaking to the United States, its string of belligerent actions — not to mention the June death of Otto F. Warmbier, the…